Process for the treatment of hydrocarbons



0611. 9, 1945. v w, 'sg uLz v 2,386,352 I PROCESS FOR THE TREATMENT OFHYDROCARBONS Filed Jan. 29, 1942 DIOLEFIN- FREE FLUI D DIOLEFINCONCENTRATE /DILUENT GAS EOLVHVdEIS GAS MIXING ZONE DILUENT GASDIOLEFIN- CONTAINING I FLUID INVENTOR WALTER A SCHULZE tion complex,which is retained on the reagent Patented- Oct. 9, 1945 raoosss i on.'rna ranamn'r or i maooannons Walter a. Schulxe, Bartles vlile, th.,assignor to Phillips Petroleum Delaware Company, a corporation ofApplication January 29, 1942. Serial No. 428,714

' 2 Claims. ((1260-6815) This invention relates to the purification ofhydrocarbons. More particularly this invention low-boiling aliphaticdiolefins from complex hydrocarbon mixturesin which they occur. Whilepresentinga process of broad application, this invention has particularreference to the separation and/or purification of conjugated dioleflns'of four, five, or more carbon atoms from hydrocarbon fluids of boilingpoints somewhat above the range of the so-called normally gaseoushydrocarbons.

Substances of the class of the diolefins and similar readilypolymerizable compounds have assumed importance because of their use asstarting materials in the manufacture of a variety-0f products of thenature of rubber and the like. As a result, dioleflns produced asby-products in hydrocarbon pyrolysis or by various specificmanufacturing processes have become increasingly valuable. This has inturn involved the development of satisfactory methods for selectivelyseparating said diolefins from complex hydrocarbon mixtures andrecovering concentrates of suitable purity for subsequent utilization.

. A number of chemical separation methods have been proposed fordioleiinv purification in which various metal salt reagents,particularly those comprising salts of the monovalent heavy metals ofgroups I and II of the periodic system. have been employed to fix thedioleflns in the form of insoluble complex salts and to eifect a primaryseparation fromhydrocarbon mixtures. Most widely used have'been variousmodifications of cuprous halide reagents,'e"specially cuprous chlorideand bromide, which form hydrocarboninsoluble addition complexes withbutadiene hydrocarbons from which the dioleilns may be recovered byheating to moderate temperatures. The efliciency of these processes hasvaried greatly, depending largely on the eifectlveness of the contactbetween the reagent and the dioleflncontaining hydrocarbon-fluid, andthe methods the reagent. Certain solid-type reagents which comprise abase of granular material, mixed for separating dioleflns from thepaneiflinic and/or olefinic components of hydrocarbon mixtures. Suchsolid-type reagents afford intimate contact with the dioletln-containingfluid; also the reagent is utilized emciently in removing the dioleilnfrom the hydrocarbon stream as the addirelates to an improved method forsegregating surface.

hydrocarbons are passed over such reagents have a signiflcantinfluenceon the purity of the recovered diolefin, and also upon the useful lifeof the reagent itself. I

Since the formation of the diolefin-cuprous halide complex upon whichthe above-mentioned separation methods depend is favored by lowtemperatures and relatively long contact time, conditions of temperatureand pressure have often been employed which may maintain normallygaseous hydrocarbon mixtures in liquid phase. While good results areobtained with easily vaporizable mixtures. such as C4 hydrocarbonfractions, certain less desirable effects appear in the treatment ofhigher-boiling mixtures containing hydrocarbons of five or more carbonatoms.

These heavier hydrocarbons have an appre-.

ciable solvent action on the cuprous halide, and liquid phase operationresults not only in small but steady losses of reagent by solution inthe liquid eilluents but also in the necessity of treating saideiliuents to remove the dissolved metal salts. Further, thenon-diolefinic hydrocarbons of lower volatility are retained on thereagent to a certain extent and are more difiicult to remove,

. e. g.,"by vaporization, without causing concurrent used for recoveringthe absorbed diolefln from losses of the dioleflns by prematuredecomposition of the dioleflnicuprous halide addition compounds. Ofcourse, if the non-dioleiinc hydrocarbons are allowed to remain on thereagent during desorption of the dioleflns, an impure product isobtained.

It is an object of this invention to provide a process for theseparation of hydrocarbon mixtures. Another object is to provide meansfor minimizing retention of non-dioleflnic hydrocarbons by metal saltreagents and/or metal saltdiolefln complexes. A further object of thisinvention is to provide a method for maintaining normally liquidhydrocarbon mixtures in vapor phase during contact with cuprous halidere- I have found that by dilution with a substantially non-condensiblegas, a dioleiln-containing hydrocarbon mixture which tends to liquefy.at

Thus, the solid reagents areefilcientby nature,.but the conditions underwhich the In one specific application, my process com prises the stepsof (l) mixing a suitably inert substantially non-condensible gas with adioleflncontaining hydrocarbon liquid to produce a vapor mixture of thedesired low dew point, (2) passing the vapor mixture in contact with asolid-type cuprous halide reagent to efiect separation of the dioleflnas the cuprous halide addition compound, and (3) heating the reagentbearing said addition compound, after removal of unreacted vapors, to

desorb and recover the diolefln.

The accompanying figure illustrates one speciflc form of apparatus forthe application of this new process. In the flrst, or absorption cycle,the hydrocarbon fluid to be processed enters the system through line Iand valve I2, passing to assassa 1' be used, with their supply andproduct lines and valves, in order to make a system operatingcontinuously. It will therefore be understood that the process may beoperated batchwise, with one reagent zone, or continuously with two ormore of said zones, depending upon the requirements of the individualinstallation.

The diluent and/or flushing gas, as used in this process, is generallyof low molecular weight and high volatility, ordinarily being asubstance which is aboveits critical temperature under operatingconditions, although this is not essential. Moreover, the gas issubstantially oxygen-free,

and inert toward either the hydrocarbon mixture or the reagent, and hassubstantially no solubility in the reagent. Suitable non-condensiblegases, for example, are methane, hydrogen, nitro' gen, and natural gassubstantially free of reactive impurities and hydrocarbons heavier thanpropane. Other gases having properties according to theaforesaidrequirements may also be usedwithin this invention.

the gas mixing zone 2, in which the hydrocarbon fluid encounters thediluent gas entering by line 29. The diluted vapor passes by line 3 toline 8 controlled by valve I, thence through cooler I and on to thereagent zone Ii via line 8, valve 8, and line I0. Throughout thisabsorption cycle, the valves 5, l2 and M are closed. The vapor passesthrough the zone ll containing a suitable metal-salt reagent, then movesvia line ll, valve The separation of such gases from the much lessvolatile hydrocarbons-under treatment at any desired point in theprocess is easily accomplished since the disparity in the boiling pointsis so great. Thus the presence of thediluent gasin the desorbed dioleflnvapor or liquid is not detrimental since the composition of this mixturepermits ready recovery of the desired components.

The diolefln-containing fluids to be treated by this process arepreferably closely fractionated it, line' H and condenser I l toseparating zone l9, wherein the diluent gas is taken overhead and thesubstantially dioleiin-free hydrocarbon liquid is removed as bottomsthrough line 20. The diluent gas passes by line 2| and line 21 tostorage 3 zone or gas holder 2|! whence it may be recycled through line29. When the metal salt in zone II is substantially completely convertedintodiolefin complex, or when absorption of diolefln decreases to anunsatisfactory level, the absorption cycle is completed, and valve 32is'closed, thus discontinuing the flow of the hydrocarbon fluid.

The diluent gas is then passed alone over thereagent in zone Ii and thenon through the separating zone is to remove small amounts ofhydrocarbons swept out of the reagent. At the end of the sweeping-outoperation, valves 4, 9 and I5 are closed and valves 5, I4 and H areopened. By this means, the gas is directed from storage zone 28 by line3, through valve 5, line i5, valve II and line ll to reagent zone If tohelp in removing dioleijins from the reagent. At the same time, aheating medium is applied to the outer Jacket of the zone ll, enteringby line 20 and leaving by line 3!. The gas-diolefln mixture passes byline l0, valve i2, line 22 and condenser 23 to separating zone 24,wherein liquiddiolefln is separated from the gas. The diolefln liquidpasses by line 25 to storage while the gas is transferred to storagezone 28 by lines 2| and 21. At the .completion of the desorptionoperation, the reagent may be cooled and used again to absorb additionalamounts of dioleflns in accordance with the first step described above.If desired a cooling medium may be passed through the jacket of zone I lduring the absorption cycle.

' In view of the foregoing description, it will be obvious that two ormore reagent zones Ii may hydrocarbon mixtures of reasonably constantcomposition which may comprise Cs hydrocarbons, although the process isobviously applicable to lighter and/ or heavier fractions within thelimits disclosed. In fact, similar condensation dimculties havebeenencountered in treating butadiene-containing hydrocarbon mixturesand have been readily overcome by the practice of this invention. Theusefulness of this invention in treating Cs and heavier mixtures isobvious. Thus, any mixture which is to be treated in vapor phase andwhich contains sufficient higher boiling components to causecondensation within the reagent vessels may be diluted withnon-condensible gas to lower the condensation temperature or dew pointto a value substantially below the temperature employed in the dioleflnabsorption. Since there is usually a margin of safety between theoperating temperature and the dew point of the diluted vapor mixture,minor composition changes are not harmful, but major changes requirerecalculation of the proportions of the vapor mixture.

The process may be operated at low pressures in the range of zero topounds per square inch. with operation between 10 and 40 pounds persquare inch ordinarily being preferred. Pressures outside these rangesmay be used in the absorption step, but no particular purpose is servedthereby, and excessively high pressures in particular may be distinctlydisadvantageous in that greater dilution of the dioleiin-containingfluid is entailed. Subatmospheric pressures are sometimes used in thedesorption operation since the decomposition of the complex may beassisted thereby.

Temperatures ranging from about 0 to about 80 F. may be used in theabsorption step, when a cuprou's chloride reagent is utilized. and it isordinarily preferred to conduct operations in the range of about 30 to60 F. At these tempera tures the diolenn complex is readily formed and Ithe following composition:

assasss satisfactorily stable. lower temperatures require greaterdilution of the liquefiable charge,

and higher temperatures may induce decomposition of the complex, so thatconditions of tem--- perimentally or calculated approximately from thevapor pressure and composition of the fluid to be vaporized. withclosely fractionated cuts the vapor pressure of the whole mixture may beconsidered, or the predominant component may 'serve as the basis forcalculation. From the vapor pressure of the said predominant componentat theeoperating temperature, alimiting maximum value for the partialpressure of the conden'sible -i'iuid in the total vapor mixture isobtained, and

sufficient non-condenslble gas is added to produce mol fractions andpartial pressures substantially below said limiting value. In general,vapor mixtures with dew points from to- 25 F. below the dioleflnabsorption temperature are preferred although still. greater differencesmay be employed if desired.

The absolute concentrations of diolefins in the vapor mixtures preparedfor treating according to'my invention will vary with the concen-.tration of dioleflns in the hydrocarbon fluids diluted and with theamount of diluent added. In general, the diolefln concentration in vapormixtures pd over the reagent may range from less than one to so per centor higher, and suitable control of the contact time is maintained togive the desired completeness of diolefin removal.

Flow rates of the vapor mixtures may range from to 600 gas volumes perhour per volume of reagent with a narrower range of about 50 to 350volumes per hour being generally satisfactory for the diolefinconcentrations usually encountered.

An 'additionalimportant feature of 'my proc is the step of passing thediluent gas alone through the reagent chamber to remove traces ofunreacted hydrocarbons adsorbed on the reagent. This assists in reducingcontamination of the desorbed diolefin concentrate by nondiolefinichydrocarbons mechanically retained by the reagent.

mixture was then discontinued and the methane alone was passed for 10minutes at 49 to 50 1''.

before the heating medium was applied to the reagent zone.v The reagentbed was then heated to 200 F. with methane still passing and the evolvedvapors were cooled and partially condensed. After separation of themethane, the product was found to be 96 per cent isoprene.

Another portion of this Cs mixture was treated in liquid phase withoutgas dilution under the same conditions as above, using-a flow rate ofabout one liquid volume per hour. The desorbed product contained only 65per cent isoprene.

Example 11 A mixture containing piperylene had the followingpomposition: 4 I

Volume percent n-Pentane .30. Pentene-2 20 Trimethylethylene 15Piperylene 35 The mixture was diluted with nitrogen in the ratio of fourparts to one to produce a vapor mixture with a dew point of 15 F. attreating pressure. I The vapor mixture was cooled to 50 F. and contactedwith solid cuprous chloride reagent at a pressure of 10 pounds gage anda rate of 300 gas volumes per hour. At the conclusion Example III Ahydrocarbon stock having the composition Volume per cent Pentene-l 52-methylbutene-1 15 Isoprene l5 n-Pentane 5 was blended with livevolumes of hydrogen per gas volume of charge stock, cooled to 60 F., and

The following exemplary operationsby the Example 1 s A crude isoprenemixture to be processed had Three gas volumes of methane were added toeach gas volume of the above mixture, and the diluted mixture having adew point of about 80 F. at 15 pounds gage was cooled to 40? I". at apressure of 15 pounds gage. This mixture was passed at the rate of about150 volumes per reagent volume per hour over a reagent comprisingcuprous chloride on asbestos until absorption became very slow. The flowof diolefln-containing dl'ogen l toe-- passed at a pressure of 25"pounds case, over a solid cupro'us' chloride reagent to separate theisoprene. Substantially no condensation occurred since the dew point ofthe vapor mixture was about 43 F. The reagent was flushed with hydrogenafter absorption had substantially eeased. Following the flushing step,the reagent bed was heated while a stream of uncooled hy- 01 through thebed, carrying out the desorbed substance. At the conclusion of thedesorption. the analysis of the product freed from hydrogen indicatedsubstantially pure isoprene.

I have thus discovered undesirable effects which accompany liquid-phaseoperation or artial condensation during vapor phase operation, 1 whicheffects cannot be eliminated merely by raising the temperature ofoperation, since that temperature is limited by the stability of metalsaltdiolefin complexes, and I have furthermore sup- 1 plied a methodwhich overcomes the dimculties involved in a wholly satisfactory manner.

The foregoing description has been particularly directed toward thepurification of mixtures comprising hydrocarbons containing nve carbonatoms. the art, however, other hydrocarbons may be treated by thisprocess merely by modification of details of operation.Furthermoraalthough cer- Aswill be perceived by those skilled in tainsolid-type cuprous halide reagents have been referred to especially inthe examples, my invention may besuccesstully applied to othermetalsalt-type reagents which form complexes with hydrocarbons. Theterms of the examples and descriptions hereinbeiore set out are not,therefore, to be construed as limitations.

The terms inert and "non-condensible" as used with reference to thediluent gas mean substantially inert toward the reagent and thehydrocarbons undergoing treatment, and non-condensible under theconditions of operation.

I claim:

1.- A process for the purification oi low-boilingnormally liquiddiolefins which comprises introducing hydrocarbons -containing same intoa stream oi an inert non-condensible gas in such proportion as to give amixture having a dew point at least 5 F. below treating temperature.-

and heating said reagent to decompose said come plex and recoverpurified dioleflns.

2. A process which comprises continuously passing an inertnon-condensible gas through a reagent zone containing a solid metal saltreagent capable of selectively retaining hydrocarbons by formation 0! athermally unstable hydrocarbon-metal salt complex, and segregatinghydrocarbons from a hydrocarbon mixture through formation of saidcomplex by (1) introducing said hydrocarbon mixture into said gas insuch proportions as to give a vapor mixture having adew-pointsubstantially below the temperature maintained in said reagent zoneduring an absorption cycle to selectively absorb hydrocarhens in saidzone through metal salt complex for- -mation, (2) stopping theintroduction of said hydrocarbon mixture to allow the flushing ofunreacted hydrocarbons from said reagent zone by said gas, (3) heatingsaid reagent zone to decompose said complex while flushing saidzone withsaid gas whereby selectively absorbed hydrocarbons are removed inadmixture with said'gas. and

(4) recovering hydrocarbons from said gas.'

WALTER A; sorrows

